Development of Reaction Model for Sinter by Examining Reduction Process of its Mineral Components

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(1) Quantitative analysis of commercial sinter before reduction by EPMA gave the contents of hematite, calcium ferrite (CF), magnetite and slag. Comparison between EPMA surface analyses of sinter before reduction and reduced to magnetite stage at 1133 K suggests that CF breaks up into magnetite and slag. Quantitative analysis of sinter during reduction to magnetite by the X-ray internal standard method using the foregoing contents reveald variations in the amount of hematite, CF and magnetite with fractional reduction ; CF was reduced at 1033 and 1133 K but was hardly at 933 nor 983 K. Microstructures of samples reduced up to magnetite stage show that CF is reduced at 1033 K but not at 983K.(2) Final fractional reduction in the hematite to magnetite stage under rising temperature conditions up to 1173 K, F_f', was measured after measuring the one at a constant temperature, F_f, both as the gas ratio CO/(CO+CO_2) = 0.20 ; CF was reduced to magnetite at 1003 K or more but was hardly below 1003 K and in the latter temperature range F_f=0.7 when the oxygen reducible in this stage was assumed to be come from hematite and CF. And the ratio F_f/F_f' is given as a function of reduction temperature, i. e. where T is the absolute temperature to obtain F_f (K). Such non-reducibility of CF at lower temperatures was confirmed at different gas rations from 0.20 to the upper limit of the magnetite stable region at 773 and 873 K.(3) Single particles were reduced stepwise in a temperature range from 753 to 1333 K and rate parameter values were evaluated in consideration of the above facts ; temperature dependencies of chemical reaction rate constant and effective diffusivity are presented.